Our phone vibrates with a Twitter notification and we do a stealth check even though we’re in a business meeting. Our heart speeds up at the sight of three new ‘likes’ on our latest Facebook status. We can’t get through the first course of our dinner without Instagramming our plate.

Grab a medium-sized object—water bottle, cell phone, book—and grip it tightly, making your hand into a fist around it. Then, without opening your fist, use that same hand to try to pick up another object. What happens? When I tried this exercise, my fist knocked uselessly against the second object and I couldn’t pick it up without opening my hand and letting go of the first object.